What will this sign be? We cannot actually say. The only Scriptural hint we know of is our Lord's own word that "the Manifestation of His Presence will be as the lightning which flashes from the one end of heaven to the other."
It may be that this will occur while men are horrified with the unnatural darkness, and that the "sign" will be a sudden and momentary cleaving of the black heavens, so that the glory of the Lord will break through, and He will, for an instant, be revealed in close proximity to earth. Will it be thus that the Jew will receive his sign from heaven?
That which follows, and which should be rendered: "Then shall all the tribes of the land mourn," points to the connection of this verse with Zechariah's prophecy: "And I will pour upon the house of David, and upon the inhabitants of Jerusalem, the spirit of grace and supplications: and they shall look upon ME Whom they have pierced, and they shall mourn for Him, as one mourneth for his only son, and shall be in bitterness for Him, as one that is in bitterness for his firstborn." Zech. xii. 10.
"And again, the manner in which Zechariah's prophecy is quoted in the Apocalypse may, perhaps, afford some slight argument in favour of the explanation of the sign suggested above, namely, that it is Christ Himself seen for a moment through a rift in the clouds, for John says, 'Behold He cometh with the clouds: and every eye shall see Him, and they also which pierced Him: and all the TRIBES OF THE LAND shall mourn because of Him.'
"Thus the Jews, although they may not as yet understand all, will at least know that it was the Messenger of Jehovah whom they slew, and that in so doing they pierced Himself. And they will mourn with no feigned lamentation, but as one mourns for his first-born, nay, his only son. All their pride will have broken down; for the word will then have been fulfilled, 'I will take away out of the midst of thee them that rejoice in thy pride, and thou shalt no more be haughty because of My holy mountain. I will also leave in the midst of thee an afflicted and poor people, and they shall trust in the name of the Lord.' Zeph. ii. 11, 12.
"Then will God look down upon the stiff-necked and rebellious people, whom long centuries of chastisement could not subdue, and lo! a remnant, broken-hearted and contrite, humbly confessing that 'all their righteousnesses are as filthy rags, that they are all fading as a leaf, and that their iniquities, like the wind, have carried them away.' They long for the personal interposition of God their Father, and cry, 'Oh that Thou wouldst rend the heavens, that Thou wouldst come down!' They are ready at last, for their Messiah. Christ has become precious to them: there is no need that He, the true Joseph, should longer refrain Himself. He had indeed said, 'Ye shall not see Me henceforth till ye shall say, "Blessed is He that cometh in the name of the Lord."'"
"But that word withholds Him no longer; for now their eyes are waiting for the Lord their God, until that He have mercy upon them: their souls are watching for Him more than they that watch for the morning."
(PEMBER'S "GREAT PROPHECIES.")
Then shall He suddenly come, "His feet shall stand in that day upon the Mount of Olives, which is before Jerusalem on the east; and the Mount of Olives shall cleave in the midst thereof toward the east and toward the west, and there shall be a very great valley, and half of the mountain shall remove toward the north, and half of it toward the south. And ye shall flee to MY valley, when He shall touch the valley of the mountain to the place He separated." Zech. xiv. 4, 5.
In this great valley of His special making it is possible, probable, that our Lord will shelter His people, while He is destroying the hordes of Anti-christ. It is of this that Isaiah speaks: "Come My people, enter thou into thy chambers, and shut thy doors about thee: hide thyself as it were for a little moment, UNTIL THE INDIGNATION BE OVER PAST. For behold the Lord cometh out of His place to punish the inhabitants of the earth for their iniquity." And when that awful judgment shall be over—"which shall burn as an oven," they shall come out of their shelter "skipping as calves of the stall." A wondrous figure of the frolicsome calves coming out of the darkness of their stalls into the glorious light, and into the full freshness of the luscious meadows.